/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Ints;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;
/**
* A high-performance, immutable {@code Set} with reliable, user-specified
* iteration order. Does not permit null elements.
*
* <p>Unlike {@link Collections#unmodifiableSet}, which is a <i>view</i> of a
* separate collection that can still change, an instance of this class contains
* its own private data and will <i>never</i> change. This class is convenient
* for {@code public static final} sets ("constant sets") and also lets you
* easily make a "defensive copy" of a set provided to your class by a caller.
*
* <p><b>Warning:</b> Like most sets, an {@code ImmutableSet} will not function
* correctly if an element is modified after being placed in the set. For this
* reason, and to avoid general confusion, it is strongly recommended to place
* only immutable objects into this collection.
*
* <p>This class has been observed to perform significantly better than {@link
* HashSet} for objects with very fast {@link Object#hashCode} implementations
* (as a well-behaved immutable object should). While this class's factory
* methods create hash-based instances, the {@link ImmutableSortedSet} subclass
* performs binary searches instead.
*
* <p><b>Note:</b> Although this class is not final, it cannot be subclassed
* outside its package as it has no public or protected constructors. Thus,
* instances of this type are guaranteed to be immutable.
*
* @see ImmutableList
* @see ImmutableMap
* @author Kevin Bourrillion
* @author Nick Kralevich
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
public abstract class ImmutableSet<E> extends ImmutableCollection<E>
implements Set<E> {
/**
* Returns the empty immutable set. This set behaves and performs comparably
* to {@link Collections#emptySet}, and is preferable mainly for consistency
* and maintainability of your code.
*/
// Casting to any type is safe because the set will never hold any elements.
@SuppressWarnings({"unchecked"})
public static <E> ImmutableSet<E> of() {
return (ImmutableSet<E>) EmptyImmutableSet.INSTANCE;
}
/**
* Returns an immutable set containing a single element. This set behaves and
* performs comparably to {@link Collections#singleton}, but will not accept
* a null element. It is preferable mainly for consistency and
* maintainability of your code.
*/
public static <E> ImmutableSet<E> of(E element) {
return new SingletonImmutableSet<E>(element);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static <E> ImmutableSet<E> of(E e1, E e2) {
return construct(e1, e2);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static <E> ImmutableSet<E> of(E e1, E e2, E e3) {
return construct(e1, e2, e3);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4) {
return construct(e1, e2, e3, e4);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5) {
return construct(e1, e2, e3, e4, e5);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
* @since 3.0 (source-compatible since 2.0)
*/
public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5, E e6,
E... others) {
final int paramCount = 6;
Object[] elements = new Object[paramCount + others.length];
elements[0] = e1;
elements[1] = e2;
elements[2] = e3;
elements[3] = e4;
elements[4] = e5;
elements[5] = e6;
for (int i = paramCount; i < elements.length; i++) {
elements[i] = others[i - paramCount];
}
return construct(elements);
}
/** {@code elements} has to be internally created array. */
private static <E> ImmutableSet<E> construct(Object... elements) {
int tableSize = chooseTableSize(elements.length);
Object[] table = new Object[tableSize];
int mask = tableSize - 1;
ArrayList<Object> uniqueElementsList = null;
int hashCode = 0;
for (int i = 0; i < elements.length; i++) {
Object element = elements[i];
int hash = element.hashCode();
for (int j = Hashing.smear(hash); ; j++) {
int index = j & mask;
Object value = table[index];
if (value == null) {
if (uniqueElementsList != null) {
uniqueElementsList.add(element);
}
// Came to an empty slot. Put the element here.
table[index] = element;
hashCode += hash;
break;
} else if (value.equals(element)) {
if (uniqueElementsList == null) {
// first dup
uniqueElementsList = new ArrayList<Object>(elements.length);
for (int k = 0; k < i; k++) {
Object previous = elements[k];
uniqueElementsList.add(previous);
}
}
break;
}
}
}
Object[] uniqueElements = uniqueElementsList == null
? elements
: uniqueElementsList.toArray();
if (uniqueElements.length == 1) {
// There is only one element or elements are all duplicates
@SuppressWarnings("unchecked") // we are careful to only pass in E
E element = (E) uniqueElements[0];
return new SingletonImmutableSet<E>(element, hashCode);
} else if (tableSize > 2 * chooseTableSize(uniqueElements.length)) {
// Resize the table when the array includes too many duplicates.
// when this happens, we have already made a copy
return construct(uniqueElements);
} else {
return new RegularImmutableSet<E>(uniqueElements, hashCode, table, mask);
}
}
// We use power-of-2 tables, and this is the highest int that's a power of 2
static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
// If the set has this many elements, it will "max out" the table size
static final int CUTOFF = 1 << 29;
/**
* Returns an array size suitable for the backing array of a hash table that
* uses linear probing in its implementation. The returned size is the
* smallest power of two that can hold setSize elements while being at most
* 50% full, if possible.
*/
static int chooseTableSize(int setSize) {
if (setSize < CUTOFF) {
return Integer.highestOneBit(setSize) << 2;
}
// The table can't be completely full or we'll get infinite reprobes
checkArgument(setSize < MAX_TABLE_SIZE, "collection too large");
return MAX_TABLE_SIZE;
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @deprecated use {@link #copyOf(Object[])}. <b>This method is scheduled for
* deletion in October 2011.</b>
* @throws NullPointerException if any of {@code elements} is null
* @since 2.0 (changed from varargs in 3.0)
*/
// TODO(kevinb): when this is removed, remember to remove from ISS and ISSFS
@Deprecated
public static <E> ImmutableSet<E> of(E[] elements) {
return copyOf(elements);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any of {@code elements} is null
* @since 3.0
*/
public static <E> ImmutableSet<E> copyOf(E[] elements) {
// TODO(benyu): could we delegate to
// copyFromCollection(Arrays.asList(elements))?
switch (elements.length) {
case 0:
return of();
case 1:
return of(elements[0]);
default:
return construct(elements.clone());
}
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored. This method iterates over {@code elements} at most once.
*
* <p>Note that if {@code s} is a {@code Set<String>}, then {@code
* ImmutableSet.copyOf(s)} returns an {@code ImmutableSet<String>} containing
* each of the strings in {@code s}, while {@code ImmutableSet.of(s)} returns
* a {@code ImmutableSet<Set<String>>} containing one element (the given set
* itself).
*
* <p>Despite the method name, this method attempts to avoid actually copying
* the data when it is safe to do so. The exact circumstances under which a
* copy will or will not be performed are undocumented and subject to change.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static <E> ImmutableSet<E> copyOf(Iterable<? extends E> elements) {
return (elements instanceof Collection)
? copyOf(Collections2.cast(elements))
: copyOf(elements.iterator());
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static <E> ImmutableSet<E> copyOf(Iterator<? extends E> elements) {
// TODO(benyu): here we could avoid toArray() for 0 or 1-element list,
// worth it?
return copyFromCollection(Lists.newArrayList(elements));
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored. This method iterates over {@code elements} at most
* once.
*
* <p>Note that if {@code s} is a {@code Set<String>}, then {@code
* ImmutableSet.copyOf(s)} returns an {@code ImmutableSet<String>} containing
* each of the strings in {@code s}, while {@code ImmutableSet.of(s)} returns
* a {@code ImmutableSet<Set<String>>} containing one element (the given set
* itself).
*
* <p><b>Note:</b> Despite what the method name suggests, {@code copyOf} will
* return constant-space views, rather than linear-space copies, of some
* inputs known to be immutable. For some other immutable inputs, such as key
* sets of an {@code ImmutableMap}, it still performs a copy in order to avoid
* holding references to the values of the map. The heuristics used in this
* decision are undocumented and subject to change except that:
* <ul>
* <li>A full copy will be done of any {@code ImmutableSortedSet}.</li>
* <li>{@code ImmutableSet.copyOf()} is idempotent with respect to pointer
* equality.</li>
* </ul>
*
* <p>This method is safe to use even when {@code elements} is a synchronized
* or concurrent collection that is currently being modified by another
* thread.
*
* @throws NullPointerException if any of {@code elements} is null
* @since 7.0 (source-compatible since 2.0)
*/
public static <E> ImmutableSet<E> copyOf(Collection<? extends E> elements) {
if (elements instanceof ImmutableSet
&& !(elements instanceof ImmutableSortedSet)) {
@SuppressWarnings("unchecked") // all supported methods are covariant
ImmutableSet<E> set = (ImmutableSet<E>) elements;
if (!set.isPartialView()) {
return set;
}
}
return copyFromCollection(elements);
}
private static <E> ImmutableSet<E> copyFromCollection(
Collection<? extends E> collection) {
Object[] elements = collection.toArray();
switch (elements.length) {
case 0:
return of();
case 1:
@SuppressWarnings("unchecked") // collection had only Es in it
E onlyElement = (E) elements[0];
return of(onlyElement);
default:
// safe to use the array without copying it
// as specified by Collection.toArray().
return construct(elements);
}
}
ImmutableSet() {}
/** Returns {@code true} if the {@code hashCode()} method runs quickly. */
boolean isHashCodeFast() {
return false;
}
@Override public boolean equals(@Nullable Object object) {
if (object == this) {
return true;
}
if (object instanceof ImmutableSet
&& isHashCodeFast()
&& ((ImmutableSet<?>) object).isHashCodeFast()
&& hashCode() != object.hashCode()) {
return false;
}
return Sets.equalsImpl(this, object);
}
@Override public int hashCode() {
return Sets.hashCodeImpl(this);
}
// This declaration is needed to make Set.iterator() and
// ImmutableCollection.iterator() consistent.
@Override public abstract UnmodifiableIterator<E> iterator();
abstract static class ArrayImmutableSet<E> extends ImmutableSet<E> {
// the elements (two or more) in the desired order.
final transient Object[] elements;
ArrayImmutableSet(Object[] elements) {
this.elements = elements;
}
@Override
public int size() {
return elements.length;
}
@Override public boolean isEmpty() {
return false;
}
/*
* The cast is safe because the only way to create an instance is via the
* create() method above, which only permits elements of type E.
*/
@SuppressWarnings("unchecked")
@Override public UnmodifiableIterator<E> iterator() {
return (UnmodifiableIterator<E>) Iterators.forArray(elements);
}
@Override public Object[] toArray() {
Object[] array = new Object[size()];
System.arraycopy(elements, 0, array, 0, size());
return array;
}
@Override public <T> T[] toArray(T[] array) {
int size = size();
if (array.length < size) {
array = ObjectArrays.newArray(array, size);
} else if (array.length > size) {
array[size] = null;
}
System.arraycopy(elements, 0, array, 0, size);
return array;
}
@Override public boolean containsAll(Collection<?> targets) {
if (targets == this) {
return true;
}
if (!(targets instanceof ArrayImmutableSet)) {
return super.containsAll(targets);
}
if (targets.size() > size()) {
return false;
}
for (Object target : ((ArrayImmutableSet<?>) targets).elements) {
if (!contains(target)) {
return false;
}
}
return true;
}
@Override boolean isPartialView() {
return false;
}
@Override ImmutableList<E> createAsList() {
return new ImmutableAsList<E>(elements, this);
}
}
/** such as ImmutableMap.keySet() */
abstract static class TransformedImmutableSet<D, E> extends ImmutableSet<E> {
final D[] source;
final int hashCode;
TransformedImmutableSet(D[] source, int hashCode) {
this.source = source;
this.hashCode = hashCode;
}
abstract E transform(D element);
@Override
public int size() {
return source.length;
}
@Override public boolean isEmpty() {
return false;
}
@Override public UnmodifiableIterator<E> iterator() {
return new AbstractIndexedListIterator<E>(source.length) {
@Override protected E get(int index) {
return transform(source[index]);
}
};
}
@Override public Object[] toArray() {
return toArray(new Object[size()]);
}
@Override public <T> T[] toArray(T[] array) {
int size = size();
if (array.length < size) {
array = ObjectArrays.newArray(array, size);
} else if (array.length > size) {
array[size] = null;
}
// Writes will produce ArrayStoreException when the toArray() doc requires
Object[] objectArray = array;
for (int i = 0; i < source.length; i++) {
objectArray[i] = transform(source[i]);
}
return array;
}
@Override public final int hashCode() {
return hashCode;
}
@Override boolean isHashCodeFast() {
return true;
}
}
/*
* This class is used to serialize all ImmutableSet instances, except for
* ImmutableEnumSet/ImmutableSortedSet, regardless of implementation type. It
* captures their "logical contents" and they are reconstructed using public
* static factories. This is necessary to ensure that the existence of a
* particular implementation type is an implementation detail.
*/
private static class SerializedForm implements Serializable {
final Object[] elements;
SerializedForm(Object[] elements) {
this.elements = elements;
}
Object readResolve() {
return copyOf(elements);
}
private static final long serialVersionUID = 0;
}
@Override Object writeReplace() {
return new SerializedForm(toArray());
}
/**
* Returns a new builder. The generated builder is equivalent to the builder
* created by the {@link Builder} constructor.
*/
public static <E> Builder<E> builder() {
return new Builder<E>();
}
/**
* A builder for creating immutable set instances, especially {@code public
* static final} sets ("constant sets"). Example: <pre> {@code
*
* public static final ImmutableSet<Color> GOOGLE_COLORS =
* new ImmutableSet.Builder<Color>()
* .addAll(WEBSAFE_COLORS)
* .add(new Color(0, 191, 255))
* .build();}</pre>
*
* Builder instances can be reused; it is safe to call {@link #build} multiple
* times to build multiple sets in series. Each set is a superset of the set
* created before it.
*
* @since 2.0 (imported from Google Collections Library)
*/
public static class Builder<E> extends ImmutableCollection.Builder<E> {
// accessed directly by ImmutableSortedSet
final ArrayList<E> contents = Lists.newArrayList();
/**
* Creates a new builder. The returned builder is equivalent to the builder
* generated by {@link ImmutableSet#builder}.
*/
public Builder() {}
/**
* Adds {@code element} to the {@code ImmutableSet}. If the {@code
* ImmutableSet} already contains {@code element}, then {@code add} has no
* effect (only the previously added element is retained).
*
* @param element the element to add
* @return this {@code Builder} object
* @throws NullPointerException if {@code element} is null
*/
@Override public Builder<E> add(E element) {
contents.add(checkNotNull(element));
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableSet},
* ignoring duplicate elements (only the first duplicate element is added).
*
* @param elements the elements to add
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@Override public Builder<E> add(E... elements) {
contents.ensureCapacity(contents.size() + elements.length);
super.add(elements);
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableSet},
* ignoring duplicate elements (only the first duplicate element is added).
*
* @param elements the {@code Iterable} to add to the {@code ImmutableSet}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@Override public Builder<E> addAll(Iterable<? extends E> elements) {
if (elements instanceof Collection) {
Collection<?> collection = (Collection<?>) elements;
contents.ensureCapacity(contents.size() + collection.size());
}
super.addAll(elements);
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableSet},
* ignoring duplicate elements (only the first duplicate element is added).
*
* @param elements the elements to add to the {@code ImmutableSet}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@Override public Builder<E> addAll(Iterator<? extends E> elements) {
super.addAll(elements);
return this;
}
/**
* Returns a newly-created {@code ImmutableSet} based on the contents of
* the {@code Builder}.
*/
@Override public ImmutableSet<E> build() {
return copyOf(contents);
}
}
}
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